Recessed ammunition primer



Jan. 16, 1968 M. F. WALTHER RECESSED AMMUNITION PRIMER 2 Sheecs sheet lFiled Aug. lo, 1966 IHIHIIIIH Ihn UIHHH Minimum l Hummm INVENTOR Jan.16, 1968 M. F. WALTHER RECESSED AMMUNITION PRIMER 2 Sheets-Sheet 2 FiledAug. lO, 1966 llllrlll/A'lllll United States Patent O 3,363,565RECESSEl) AMMUNI'HON PRIMER Mark F. Walther, Newburg, Md., assigner tothe United lSqtates of America as represented by the Secretary ot' theFiled Aug. 10, 1966, Ser. No. 571,654 Claims. (Cl. 102-46) ABSTRACT 0FTHE DISCLOSURE There is disclosed an ammunition primer which has arecessed contact button to avoid accidental contact by other objectsduring handling of the ammunition and prevent the possibility of straycurrent tiring the primer and setting oif the change. The improvementrequires a more slender tiring pin and permits sliding contact betweenthe button and pin, allowing the button to be stopped during its travelrather than on its end for the purposes of safety.

The invention described herein may be manufactured and used by or forthe Government of the United States of America tor governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates generally to the ordnance art and, moreparticularly, to an ammunition primer for a cartridge which primer isdesigned to obviate inadvertent ignition of the propellant charge byeither physical or electromagnetic means.

Currently, most ammunition primers utilize a contact button which issubstantially ilush with the aft end of the projectile case. Thisconstruction has proven to be both undesirable and even dangerousbecause, during the course of handling the ammunition, .premature ringmay occur if some object other than that specifically provided forfiring should impinge upon the contact button. More importantly, inelectrical tiring systems where a primer mixture is used which iselectrically conductive, stray electromagnetic energy may accidentallyheat the mixture to its ignition temperature and, upon deagrationthereof, the evolution of the hot solids and gases would ignite thepropellant in the cartridge case to prematurely fire the slug.

Among the techniques used to prevent inadvertent ignition of ordnanceignition elements are filters and safety switches. For gun ammunitionthese methods are too cumbersome. For those ordnance components whichare not permanently connected to the firing circuit but utilize a movingfiring pin, techniques of construction can be employed as hereindescribed to avoid the possibility of premature ignition.

Accordingly, it is an object of the present invention to suicientlyshield the contact button in ammunition primers in order to guardagainst the possibility of a premature firing of the projectile.

Another object of the present invention is to recess the contact buttonin ammunition primers in order to render them safe from strayelectrostatic or electromagnetic energy which might ignite the primermixture.

A further obect of the present invention is to provide a recessedammunition primer for machine gun ammunition which may be tiredelectrically and which permits better contact with the tiring pin.

A still further object of the present invention is to provide anammunition primer which has a recessed contact in an electromagneticallyshielded hole which will avoid the chance of unintentional tiring andwhich will permit sliding contact with a tiring pin rather than on itspoint.

A still further object of the present invention is to provide anammunition primer whose contact means is sufficiently recessed Within ametallic cup, such cup acting as a Faraday cage in significantlyattenuating stray electrostatic and electromagnetic energy which mayproduce inadvertent firing.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingswherein:

FIG. l is a partial longitudinal section of the aft portion of theammunition case showing a primer assembly in accordance with the presentinvention, a portion of the breech block and firing pin also beingshown;

FIG. la is a section taken along line liz-1a of FIG. 1 showing itscontact means;

FIGS. 2 through 8 are views similar to FIG. 1 showing variousembodiments of the recessed ammunition primer of the invention without ashowing of the breech block and firing pin or cartridge case; and

FIG. 4a is a section taken along la-4a of FIG. 4 showing its contactmeans.

The present invention is basically directed to a means for improvingupon the conventional ammunition cartridge in such a manner that, alongwith a slight change in typical tiring pin contours, it can be usefulfor purposes of electrical machine gun tiring or conventional guns usingan anvil type primer.

Referring now to the drawings wherein like'reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIG. l a primer cup 11 centrally disposed withinpocket or cavity 15 formed at the aft end of the cartridge 12 whichcontains the propellant charge 13. Primer cup 11 is formed with arelatively small central hole in its base and lies ilush with the aftface of cartridge 12. Within the rearward portion of cartridge 12 is anelectrically conducting contact button 14 which is dish-shaped in amanner that its central portion is spaced farther from the cartridge aftface than its side portions. Contact button 14 is separated from primercap 11 by an insulating member 16. The insulating means throughout theseveral views may be of plastic or rubber or some other substancesuiiiciently resilient to absorb the back pressure upon detonation ofthe charge. A washer 25 is disposed between con tact button 14 andprimer cup 11 as an extension of insulating member 16 and shaped so asto lit snugly within button 14. The central hole in washer 25 is alsorelatively small and is in axial alignment with the hole in primer cup11. A thin paper disc 17 may be pressed into cup 11 during assembly inorder to compact primer mixture 18 within the primer assembly 10. A cupsupport 19 is seated Within cup 11 and protrudes slightly therebeyond incavity 15. Cup support 19 is provided with a central aperture 20, sothat upon ignition of mixture 18, the hot gases and solids will rupturedisc 17 and pour forth through aperture 2l) to initiate propellant 13 incartridge 12. It should be noted that cup support 19 serves to preventthe collapse of cup 11 and to retain the primer mixture 18 properly inplace.

Propellant charge 13 which propels the slug of the ammunition, ofcourse, lls the cavity 22 of the cartridge 12. Propellant charge 13 isin direct communication with the space Within cup support 19 by means ofa spit hole 21.

Seated centrally within the disheshaped contact button 14 and spotwelded thereto, is an electrically conducting contact memher 23. Thismember may be made of brass or its equivalent and may be circular or asin FIG. la square-shaped having its four corners or ears 23a bent up andaround a resilient spacer-washer 24 at assembly. Washer 24 is primarilyfor the purpose of maintaining ears 23a spaced from its base throughoutsliding contact with the tiring pin.

The forward end of a portion of a typical breech block 28 is shown witha ring pin 26 commencing entry into primer assembly through its nose2'7.

In operation, the ring pin 26 is electrically tired by some suitablemeans, not shown, within its breech block 28 whose bored end is incontact with the aft end of cartridge case 12. The firing pin 26 is ofconventional design except for its nose 27 which is modiiied into aslender profile. Upon tiring, nose 27 enters primer assembly 10 throughthe hole in the base of primer cup 11 which is smaller than normal inorder to increase the electromagnetic shielding. This hole is, however,large enough to receive nose 2'7 without interference throughout tiringpin entry. As the pin continues on its travel, it expands the small holein washer 2S, since the washer hole is slightly smaller than the primercup hole. As the pin 26 nears its final position where it will seat inthe breech block 28, it makes contact with contact member 23, therebypassing current through button "I4 and igniting mixture 18. Such contactis made not through the blunt end of nose 27, but rather by a slidingand scratching of the nose with the tips of ears 23a. FIG. la shows inphantom the nose 27 in contact with member 23. This sliding orscratching communication with Contact member 23 results not only in abetter contact but it tends to reduce breakage of the tiring pin nose 27after repeated use.

From the above design, it is apparent that the likelihood of any strayelectrostatic or electromagnetic currents which would initiate mixtureIS has been greatly reduced since the primer cup 11 acts in effect as aFaraday cage which, in the presence of electromagnetic energy, willabsorb most of the electric charge and effectively shield the contactmeans, so long as the tiring pin or other means is not projectingthrough the aperture in cup 11 during such presence. Also, it should benoted that because of the low current density of cup 1I in the vicinityof mixture 18, ignition of primer I8 therethrough is of little concern.

Turning now to FIG. 2 of the drawings, another embodiment 101 of aprimer assembly is shown wherein insulating means or cups 31, 32 ofthermosetting plastic and cups 11, 29, 3G and 19 of brass are seatedwithin each other and pressed together to form the primer assembly 101.Primer cups 11 in all the figures except 6 are similar. Insulating cup31 in this figure as well as in FIGS. 3, 6 and 8 is formed with athrough bore of the same dimension as that of the bore in cup Il.. Cup29, FIGS. 2, 3, 6 and 8, acts as the Contact member analogous to that ofmember 23 in FIG. 1. It is constructed with radial cuts, not shown,around a central hole 2%: in order to facilitate the insertion andwithdrawal of the tiring pin nose 27. As in FIG. l, contact is slidinglymade with the pin rather than on its end. Cups 32, FIGS. 2, 3, 6 and 8,are provided with a central cavity and each are so disposed behind hole29a so as to accommodate the tiring pin as it passes through the contact29. This cup acts to keep cups 29 and 3?, FIGS. 2, 3 and 6, in a spacedapart relation with the latter acting as a contact button for mixture1S.

In FIG. 3, primer assembly IGZ differs only from assembly 101 in thatthe former has an additional cup 33 which is similar in construction tocontact 29 except that it is larger. A rubber gasket 34 is provided inthis embodiment between cups 11 and 33, or as an alternative, aninsulated coating may be applied to cup 33. VJhen the tiring pin entersprimer assembly B02, the cup 33 folds over inwardly and remainsinsulated from the ring pin by means of gasket 3d which remains incontact with the folded-over portion of cup 33. ln this embodiment,maximum shielding protection is achieved by means of cup 33.

In FIGS. 4 and 4a, primer assembly lr03 differs from the aforementioned.designs in a manner in which the contacts are formed. Here, a `plasticinsert 37 of thermosetting material, circular or square in crosssection, as shown, is c provided with a cavity at its one end foraccommodating the entrance of the ring pin. Insert 37 is also providedwith slots in each of its sides. The contact means in this design iscomprised of a plurality of electrically conducting C-shaped members 35with one leg of each being inserted into one of the respective slots.The length of each leg is equal to one-half the width of insert 37 lessone-halt the leg width. Therefore, the inserted legs collectively forman aperture 35a, clearly shown in FIG. 4a, through which the ring pinnose 27 may slidingly protrude. The contacts 35 are held in place byplastic collar 36 which serves also to insulate contacts 35' from primercup il. The other legs ot members 35 are fully exposed to mixture I8 forpurposes of conducting electric current thereto.

in FIG. 5, primer assembly lil., consists of a minimum of parts whereina contact disc 33 is simply molded centrally in a plastic hat-shaped cup39 whose cavity opens toward the primer cup 11 base hole in order toaccommodate entrance of the tiring pin. Cup 39 serves also to insulateinsert 38 from cup 11. A centrally disposed hole 38a in contact 38serves to slidingly receive nose 27 in the same manner as theaforementioned contacts. I-Iere cup 4t) serves the same purpose as cup19 in the other embodiments except that it is contoured in a manner tomaintain a relatively constant cross-section of the space in which theprimer mixture 18 occupies. Hole 41 is formed for the same purpose ashole 20 ofthe other designs.

In FIG. 6, primer assembly differentiates from the design shown in FIG.2 only by the introduction of a means for obtaining a smaller primer cupopening. Such is achieved by a rubber washer 43 which, when assembled inthe aft portion i211 of primer cup 42, is sutiiciently constricted toeffectively shield hole 29a in Contact member 29. Upon entry of thetiring pin, washer 43 will yield to permit sliding contact with member29.

The primer assembly 106 of FIG. 7 is a design which provides a certainamount of shielding by means of insulation 44 in the form of a plastictube involuted at one end in a manner to mate with contact button 45which is a brass disc, or its equivalent, having an extension 45a on oneside thereof around its periphery. This involuted tube presents anopening centrally located and of a diameter equal to that of the hole inprimer cup 11. In this embodiment only, the blunt end of the tiring pinnose 27 contacts button 4S as it passes through the hole in primer cup1I.

Disc 17 in the embodiments shown in FIGS l, 2, 3, 4, 6 and 7 is of thesame design and functions for the purposes mentioned in the descriptionof FIG. l. Disc 17a is different only in that it assumes a shape similarto cup 40.

Referring now to FIG. S, the recessed ammunition primer of the presentinvention is shown as applied to the Wire bridge-type initiator used insome ammunition cartridges. In this embodiment 107, an electrode 4S ofbrass or other suitable material is disposed forward of insulation cup32 with a portion 48a thereof tted within cup 29. In order to insureproper contact with the electrode, a circumferential groove 29h may beprovided in cup 29. An insulating washer 46 is disposed betweenelectrode .3 and a brass cup 51 while an insulation cup 47 separates awire bridge support cup 50, of brass or other suitable material, fromthe electrode. Attached to the forward face of the electrode is atypical nose piece to which is secured, as by welding, the wire bridge49, of wire strips attached at one end thereof to the nose and at theiropposite ends to cup Sti. Primer mixture 18, which surrounds wire bridge49, is ignited by the bridge wires via electrode 48 and cup 29. Alongthe circumference of cup 51, a groove Sila may be provided similar tothe one on cup 29, thereby maintaining the integrity of the primerassembly.

From the foregoing descrip-tion, it is apparent that an ammunitionprimer for a cartridge has been designed which provides a limitedexposure of the ammunitions electro-explosive Contact to the environmentby means of a recessed primer disclosed in several embodiments. The

principal advantage of the present design is the ability to use theammunition with increased safety and with less regard to strongelectromagnetic influences. rl`his design is unique and offersadvantages over prior designs because a recessing of the primer buttonhas been provided which not only protects the primer from environmentalinfluences but it also permits sliding contact with a tiring pin ratherthan contact on its point While effectively shielding the contact meansagainst stray electromagnetic energy. A more slender tiring pin istherefore warranted which assures better contact for ignition.Furthermore, because of the slenderness of the firing pin and itsability to enter the primer assembly before making contact, stoppage ofthe firing pins travel becomes more feasible. lt might also be possibleto design a machine gun system wherein a locking of the breech `blockmay be made while t-he pin is moving to thereby create an automaticdelay Without separate synchronizing switches.

The present invention provides a simple solution for guarding againstaccidental ignition due to electrostatic or electromagnetic energy bymeans of a Faraday shield not heretofore `conceived for ammunitionprimers which effectively prevents premature firing. Also, the design isinexpensive, easy to manufacture and simple in operation.

Although the invention has been described in terms of electric firingdevices, it is not to be so limited since the subject recessedammunition primer is capable of use in any percussion type cartridge.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that Within the scope of the appended claims the inventionmay be practiced otherwise than as specically described.

What is claimed is:

1. A recessed ammunition primer in a cartridge comprising:

a primer cup disposed centrally within the primer pocket formed at theaft end of the cartridge, said cup having a small central hole in itsbase;

electrically conductive contact means inwardly spaced within said primercup;

electrically conductive explosive primer mixture disposed inwardly ofsaid contact means; and

a first means to shield said contact means from environmental influencesand at the same time allow a firing to be effected only by means of atiring pin sufliciently slender to enter the axially aligned holes forcontacting said contact means said first shielding means comprising:

a first insulating means for maintaining the spacing of said contactmeans within said primer cup by being disposed substantiallytherebetween and said first insulating means having a small centralopening in axial alignment with said cup base hole.

2. The primer of claim 1 wherein said contact means comprises adisc-shaped contact button and said iirst insulating means comprises atube involuted at one end for support of said button.

3. The primer of claim 1 wherein said contact means comprises adish-shaped contact button and a contact member seated within saidbutton, said contact member having extension means thereon, whereby asliding contact may be made by the firing pin with said contact memberextension means.

4. The primer of claim 1 wherein said contact means comprises a firstcup centrally disposed within said primer cup and having a small centralhole in its base, an electrode contacting said rst cup, wire bridgemeans secured to said electrode, said wire bridge means comprising awire bridge support cup and a Wire bridge in direct communication withsaid primer mixture, second insulating means disposed between said firstcup and said electrode, and third insulating means disposed between saidsupport cup and said electrode.

5. The primer of claim l wherein said contact means comprises a rst cupcentrally disposed within said primer cup and having a small centralhole in its base and a Second cup seated within said rst cup, secondinsulating means disposed between said iirst and second cups, saidsecond insulating means being provided with a central cavity directlybehind said iirst cup base hole, whereby sliding Contact by the tiringpin may be made with said contact means through said base hole.

6. The primer or" claim 5 and further including a means for additionallyshielding said contact means.

7. The primer of claim 6 wherein said additional shielding meanscomprises a third cup centrally disposed Within said primer cup andsubstantially contiguous thereto, said third cup having a central holein its base smaller than said primer cup base hole, and third insulatingmeans disposed between said third and primer cups in the vicinity oftheir respective base holes, whereby the region of said third cup aroundits base hole will fold over and remain insulated from the firing pinupon its entry into the primer.

8. The primer of claim 6 wherein said additional shielding meanscomprises a rubber washer disposed between said first insulating meansand said primer cup at the vicinity of said primer cup base hole, saidwasher having a closed central hole therein in axial alignment with saidprimer cup base hole which central hole is made to open upon entry ofthe firing pin into said primer.

9. The primer of claim ll wherein said first insulating means comprisesan insert having a cavity at one end thereof opening toward said primercup base, part 0f Said insert cavity forming said insulating meansopening, said insert also having slots extending through the wall ofsaid cavity, said contact means comprising a plurality of C- shapedstrips with one leg of each said strip being received Within respectiveones of said insert slots to collectively form an aperture forfacilitating a sliding firing pin contact, and said first insulatingmeans being comprised further of a collar for maintaining said strips inplace.

10. The primer of claim 1 wherein said rst insulating means comprising ahat-shaped cup with its cavity forming part of said insulating meansopening, and said contact means comprising a disc transversely disposedwithin said hat-shaped cup, said disc having a central slot therein,whereby sliding contact by the firing pin may be made with said contactmeans through said disc slot.

References Cited UNITED STATES PATENTS 2,299,466 10/1942 Coffman.2,458,478 1/1949 Maneval l02-70.2 X 3,090,310 5/1963 Peet et al IGZ-86.5 X

BENJAMIN A. BORCHELT, Primary Examiner. SAMUEL W. ENGLE, Examiner. G- H.GLANZMAN, Assistant Examiner7

